Sound reverberating device



June 8, 1965 A. J. JANISIO souun REVERBERATING DEVICE I5 Sheets-Sheet 1 Filed Jan. 18, 1962 AUDIO AMPLIFIER 34 3'42:

AUOIO AIPLIFIER AUDIO AMPLIFIER 44 AUDIO SIGNAL GENERATOR AND AMPLIFIER RECORD PLAYER TUNER I.

TAPE DECK 2O INVENTQR. flaam d. clan/s10 June 8, 1965 A. J. JANISIO 3,188,339

SOUND REVERBERATING DEVICE Filed Jan. 18, 1962 3 Sheets-Sheet 2 INVEIYTOR: fiaam d. c/am/ 5/0 United States Patent 3,188,389 SOUND REVERBERATING DEVICE Adam J. Janisio, 3813 Bernard St., Chicago 18, Ill. Filed Jan. 18, 1962, Ser. No. 168,312 Claims. (Cl. 179-1) The present invention generally relates to the synthe sizing of sound reverberation effects of the type which naturally occur when sound waves are radiated in large music halls, auditoriums and the like. More particularly, it relates to a method and an electronic system for producing such effects and it further relates to a time delay struments to the ear of the listener, as well as similar sound waves which reach the listeners car only after undergoing one or more reflections from the surrounding structures. The effect of such reflected waves is to enrich the quality of the sound and this phenomenon is known as reverberation. Either too much or too'little reverberation in a musical production is unpleasantand, accordingly, it has been the practice in the past to design music halls and the like to provide an acceptable degree of reverberation.

Since much recording of music can best be done in rooms having substantially no reverberation, it would be desirable to provide means for artifically producing reverberant effects. It has been found that the illusion of depth and spaciousness in sound waves can be synthesized by time delaying a portion of the sound signal and superimposing it upon the basic signal. The time delay is controlled so that the delayed signal lags the basic signal by a phase angle comparable to that at which naturally produce reverberant sound waves lag the original or basic waves. Although in the case of a sound recording or a broadcast the time delayed signal can be introduced prior to recording or transmission of the signal, I prefer to introduce such signal in the form of a separate sound wave rather than as an audio electric signal to avoid any noticeable intermodulation between the basic sound signal and the delayed sound signal. Another advantage of maintaining the two signals separate prior to transducing them into actual sound waves is that adjustment of the relative amplitudes of the two signals can be made by the individual listener to his own liking.

In the past, various attempts have been made to provide the required delay in the audio signal to provide a reverberation effect, but for the most par-t, these attempts have either failed altogether, or have resulted in rather complex and unwieldy structures whose very size prevents their application to relatively small sound systems,

a new and improved electromechanical device for delaying a sound signal.

Another object of the present invention is to provide a new and improved device for artificially producing sound reverberation effects, which device is small in size, compact and sturdy in construction, is relatively inexpensive to manufacture and 1s adaptable to many electronic sound systems now in existence.

A still further object of the present invention is to provide a new and improved sound reverberation device for use in a stereo type of sound reproducing sysetem.

The above and further objects and a better understanding of the present invention may be had by reference to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates an electric circuit, in block diagram form, for synthesizing reverbatory sound efiects in accordance with one aspect of the present invention;

FIG. 2 is another electric circuit, in block diagram form, illustrating the application of certain aspects of the present invention to an electronic instrument such, for example, as an electronic organ;

FIG. 3 is an elevational view of an electromechanical time delay device embodying certain features of the present invention;

FIG. 4 is a longitudinal, sectional view of the device of FIG. 3, taken substantially along the center line thereof;

FIG. 5 is a cross-sectional view of the device of FIG. 3 taken along the line 5-5 of FIG. 4;

FIG. 6 is a schematic electric circuit diagram illustrating the manner in which the time delay device of FIGS. 3, 4 and 5 may be connected in an electronic sound reproducing system;

FIG. 7 is an elecational view of an alternative embodiment of the present invention which finds particular application in a multiple channel sound reproducing system such, for example, as is commonly used for stereo effects;

FIG. 8 is a sectional view ofqthe device of FIG. 7 taken along the line 8-8 thereof;

FIG. 9 is an electric circuit diagram illustrating one manner in which the time delay device of FIGS. 7 and 8 may be connected into a multiple channel sound reproducing systemrand FIG. 10 illustrates, in block diagram form, a multiple channel sound reproducing electronic system incorporating the time delay device of FIGS. 7 and 8.

Before referring to the drawing illustrating the present invention in detail, it should be understood that the present invention is readily adaptable to almost any kind of electronic sound producing or reproducing system in which an electric signal within the audio range is converted to sound waves by any suitable transducer such, for example, as a conical type of loud-speaker. As such, the present invention is applicable to musical instruments of the electronic type such, for example, as organs and electric guitarsato devices such as radios and television receivers; and to electronic devices for playing back prerecorded music such, for example, as record players and tape recorders. Moreover, the electromechanical time delay device of the present invention finds use in many other applications where a controlled time delay of a low frequency signal is required.

Referring now to the drawings and particularly to FIG. 1 thereof, there is shown, in block diagram form, a system for synthesizing sound reverberatory effects in a monaural electronic sound reproducing system. As will become clearer as this description proceeds, the time delay device and associated equipment of the present invention may be initially incorporated into electronic sound producing systems at the time of their manufacture or it may be readily added as auxiliary equipment to systems previously in use. The system shown in FIG. 1 comprises a main or principal loud-speaker 20 which is driven by an audio-electric signal supplied thereto from a suitable audio amplifier 22 which comprises a suitable number of stages to amplify an audio signal supplied thereto from any one of a plurality of suitable devices such as the record player 24, the tuner 26 or the tape deck 23 to a sufficiently strong signal to drive the loud-speaker. As thus far described, the circuit of PEG. 1 is entirely conventional, and in order to enrich the sound produced by this system there is provided in accordance with the present invention, time delay means for delaying a portion of the output signal from the audio amplifier 22 and supplying it to one or more of a plurality of auxiliary loud-speakers 3t 31 and 32. The loud-speakers 3t 31 and 32 are disposed in the same general area as is the loudspeaker 24 so that the time delayed sound waves produced by the speakers 36, 31 and 32 are superimposed on the sound waves produced by the principal speaker 29, thereby creating the desired reverberatory effects. Inasmuch as only a single loud-speaker is required in order to produce the reverberatory sound waves, only the speaker 30 has been shown in solid lines, but under some conditions the reverberatory effect can be enhanced by the use of additional speakers strategically located with respect to one another, to the principal speaker 26 and to the physical environs. Hence, the speakers 31. and 32 have been shown in phantom.

The loud-speaker 3t) and any additional speakers such as the speakers 31 and 32 are preferably connected either in parallel or in series in an out-of-phase relationship and are driven by means of an audio amplifier 34 which preferably includes a suitable volume control, shown schematically at 35, for enabling manual adjustment of the volume of sound waves produced by the reverberatory speakers 30, 31 and 32 relative to the volume of the basic sound waves produced by the loud-speaker 2t). As more fully described hereinafter, such volume control may be included elsewhere in the reverberatory portion of the system if desired.

The input signal for the audio amplifier 34 is derived from the output terminals of an electromechanical time delay device 37 which may, for example, be an electromechanical time delay device of the type more fully described hereinafter in connection with FIG. 3. The input to the time delay device 37 is an electric signal representative of the sound waves being generated by the loudspeaker 2i) and which, as shown, may be suitably taken from the output of the amplifier 22. Although the input signal to the time delay device 37 could be extracted from some other point in the system ahead of the power output, since the signal has a maximum energy level at the output of the amplifier 22, it is normally preferable to make the signal tap at this point.

It will be noted that in the device of REG. 1 a separate audio amplifier 34 and a loud-speaker or speakers are provided for producing the time delayed sound Waves. This produces the most desirable reverberation effects with a minimum of distortion. However, in those applications where it becomes important to minimize the manufacturing cost of the system and a compromise in the quality of the reproduced sound can be tolerated, the auxiliary loudspeakers Sti, 31 and 32 can be eliminated and, at least, the power stage of the amplifier 34 can also be eliminated. In such a system, the electric output signal from the time delay device 37 is fed back to the amplifier 22 by suitable coupling means well known in the art, so that both the original sound signal and the time delayed sound signal are superimposed in the electric circuit of the amplifier 22 and simultaneously supplied to the loud-speaker 249. Of course, with such a system some intermodulation frequencies will be produced with a resultant amount of distortion and the cost of completely eliminating such distortion will, in most instances, be greater than the cost I of utilizing a separate audio amplifier and loudspeaker for producing the time delayed sound waves.

Referring now to FIG. 2, there is shown an electric circuit diagram in which the teachings of the present invention are embodied in an electronic musical instrument.

In this system a complex audio electronic signal is generate-d by means of suitable circuits in an audio signal generator and'amplifier 4t) and connected to a loud-speaker 42 which converts the electric signal into sound waves. A portion of the electric signal appearing at the output of the unit it is connected to the input of a suitable time delay device 42, the output of which is amplified in an audio amplifier 44 which drives a conventional loud-speaker d6. It will be readily apparent to those skilled in the art that the system of FIG. 2-is basically the same as that of FIG. 1 and that where desired additional loud-speakers can be connected in parallel or in series with the speaker 46 to enhance the reverberatory efiect. Moreover, if desired, the principal loud-speaker 42 may be used for producing both the basic sound waves and the time delayed sound waves in the manner described hereinbefore in connection with the circuit of FIG. 1.

Referring now to FIGS. 3 and 4, there is shown an electromechanical time delay device 59 having a pair of electric input terminals 52 and 54 and a pair of output leads 56 and 58. An electronic audio signal to be delayed is applied between the terminals 52 and 54 and is thus conducted via a pair of leads 6t) and 62 to the helical coil 64 of an electromagnetic driver 65 of the type commonly employed for driving the cone of a loud-speaker.

As such, the electromagnetic driver 65' includes in addition to the coil 64 a permanent magnet 66 which is suitably secured to a cup-shaped housing member 67 which is formed of a paramagnetic material and forms part of the magnetic circuit for the permanent magnet 66. A ring 68 also formed of paramagnetic material is secured to the lip of the housing 67 and has a reentrant annular flange 69 which extends a short distance into the housing 67 to provide a relatively long cylindrical surface 70 extending opposite a cylindrical external surface of the magnet 66. The coil 64 is wound on a very thin and light cylindrical coil form or spider 72 which is secured to a generally circular diaphragm 74 whose marginal edge is fixedly connected to 'a diaphragm support ring 76 which, in turn, is secured to the ring 68. If desired, the rings 68 and 76 can be made as a single, integral unit. The permanent magnet 66 is magnetized in an axial direction extending.

from left to right in FIGS. 3 and 4 of the drawing and, consequently, current flowing through the coil 64 cuts the magnetic flux of the magnet 66 causing the coil 64, together with the coil form 72 in which it is wound and the diaphragm '7 4, to move axially of the magnet 66 in accordance with the wave form of the current supplied to the coil 64.

In order to avoid excessive loading of the movable parts of the system as thus far described, the diaphragm 74 is provided with a plurality of apertures 80 in the central portion thereof to permit air to flow freely into and out of the housing 67. If the apertures 80 were to be omitted, movement of the diaphragm 74 towards the magnet 66 would be restricted. It will be apparent to those skilled in the art that the electromechanical driver 65 as thus far described may be obtained by removing the speaker cone from a conventional permanent magnet loud-speaker. It will also be apparent that the diaphragm 74 and the coil form 72 will move back and forth in an axial direction relative to the magnet 66 in direct correspondence to the shape of the wave form of current applied to the coil 64. Hence, the electric signal which corresponds to the basic sound wave is converted in the device 65 from an electric current to a longitudinal, mechanical vibration.

In accordance with an important feature of the present invention the mechanical vibration of the diaphragm '74 is coupled to another permanent magnetic device 82 which reconverts the mechanical vibrations into an electric'current having a wave form corresponding to the shape of the mechanical waves supplied thereto. Accordingly, the unit 82 is essentially a microphone, and in the illustrated embodiment of the invention it comprises a cup-like housing 83 on the inner bottom wall of which is mounted a U-shaped permanent magnet 84 having a pair of poles $6 and 88, respectively. The housing 83 can comprise a U-shaped nonmagnetic bracket, if desired. A pair of serially connected coils and 92 are respectively wound on the legs of the magnet 84 and a lightweight, thinwalled, tempered diaphragm 94 formed of a paramagnetic material is secured over the open-end of the housing 83. As shown, the marginal edge of the diaphragm 94 is fixedly secured to the relatively rigid housing 83, whereby the central portion of the diaphragm 94 is free to move towards and away from the magnetic pole faces 86 and 88. As will be apparent to those skilled in the art, movement of the diaphragm 94 towards and away from the poles 86 and 88 alters the reluctance of the magnetic circuit thereby generating a voltage in the coils 90 and 92 which are series connected by means of a conductor 96. Accordingly, the unit 82 converts mechanical vibrations supplied to the diaphragm 94 into an electric current flowing in the conductors 56 and 58, which current has a wave shape corresponding to that of the mechanical vibrations applied to the diaphragm 94. As pointed out above, the unit 82 functions as a miprophone and a modified conventional magnetic earphone may be used in its stead, if desired.

' In order to couple the mechanical vibration of the diaphragm 74 of the driver unit 65 to the diaphragm 94 of the microphone unit 82, and in order to introduce a predetermined time delay in such signal, there is provided in accordance with the present invention a mechanical coupling device including a very light coil spring 100 bonded at one end to the diaphragm 94 and at the other end to the diaphragm 74. The spring 100 is directly secured to the diaphragm 94 but is indirectly connected to the diaphragm 74 by means of a rigid, nonmagnetic connector 102 having a tubular section 103 to the end of which the end of the spring 100 is suitably bonded. The connector 102 has a flange portion 104 whose surface conforms closely to the shape of the diaphragm 74 and which is secured thereto. In order to accurately transmit the frequencies appearing in the upper portion of the audio spectrum it is important that the mechanical coupling unit be relatively light in weight and, therefore, it has been found that the best means of securing the spring and the connector 102 to the diaphragms 74 and 94 respectively is by means of plastic cement.

In order to provide the requisite time delay in a small compact device, the time delay device of the present invention causes the induced vibrational wave to be translated from the left-hand end of the spring 100 as viewed in FIGS. 3 and 4 to the right-hand end in step-bystep fashion. To this end, there is provided a damping block or bar 106 which is formed of a soft, resilient ma terial such, for example, as sponge rubber, mounted within the spring 100 and extending axially thereof. The right-hand end 107 of the block 106 as shown in FIG. 4, is secured as by means of cement to the diaphragm 94 and the left-hand end 108 as shown in FIGS. 3 and 4, is spaced a short-distance from the end of the connector 102 for the purpose of permitting air to pass in and out of the unit 65 through the apertures 80 thereby to reduce the mechanical loading on the device 65. As best shown in FIG. 5, the block 106 has an unstressed diagonal dimension exceeding the internal diameterof the spring 100. Accordingly, the block 106 is transversely compressed within the spring 100 to insure good mechanical coupling betwen the block 106 and the spring 100. The length and width of the block 106 are, however, less than the internal diameter of the spring 100 so that only the corner edges of the block 106 physically engage the spring 100with the intermediate sides of the block 106 being spaced from the turns of the spring 100. As best shown in FIG. 5, this arrangement results in the spring 100 engaging the block 106 at something less than once every quarter of a turn of the spring. Hence, the portions of i the spring 100 intermediate the areas which contact the block 106 are free to vibrate in a relatively undamped .condition and the, axial vibration induced by the driver 65 passes along the spring 100 to the diaphragm 94 in step-bystep fashion thereby to provide a substantial time delay in a relatively short unit. In addition, the damping block 105 eliminates wave reflections from the ends of the spring 100 whereby no additional damping devices are required.

The time delay provided by the unit 50 is proportional to the length of the spring 100 and damping block 106 and as the length of the spring 100 is increased the amount of time delay iscorrespondingly increased. Although the spring constant of the spring 100 and the hardness of the block 106 might also be increased to increase the time delay of the device, this results in an increase in the load on the driver 65 and microphone 82 and should be avoided. In order to provide most efiicient operation, the unit 50 should be mounted in a vertical direction with the microphone at the top.

As indicated hereinabove, it is most desirable that neither the driver 65 nor the microphone 82 be mechanically loaded and consequently the devices. 85 and 82, respectively, are spaced apart by a distance exactly equal to the total length of the spring and connector 102, so that the spring is neither in tension nor compression. To this end there is provided a support bracket having a base portion suitably secured as by two or more wood screws 112 to a wooden support member 113 which may form a portion of the cabinet of the device with which the. unit 50 is used and a pair of upstanding portions 114 and 116 to which the devices 65 and 82 are respectively connected by means of suitable screws 118 and 120.

If the unit 82 is not mounted in a metal cabinet, it should be shielded by a'metallic hood to prevent the pickup of stray electro-magnetic fields, such as. those generated by power lines and especially power transformers, to which the microphone is very sensitive.

A most desirable characteristic of the time delay device 37 is that it can be connected to the low output impedance terminals of the audio amplifier 22 so, as not to appreciably load the output circuit of the audio amplifier. Accordingly, the power requirements of the system are not substantially increased by incorporating the reverberatory system of the present invention therein. In one device built in accordance with the present invention only a few milliwatts is required to drive the time delay device.

In a device built in accordance with the teachings of the present invention the following specifications have been found to produce highly satisfactory results:

Spring 100 .020 inch diameter piano wire' Pitch=l5 turns/inch Inside diameter yie inch Length=2 inches 7 Block 106 Commercial soft foam rubber Length=1 inches Cross section-= 4 inch square It has been found that reverberation of the very low audio frequencies is not necessary in order to synthesize normal reverberant effects and, therefore, there is provided in accordance with another feature of the present invention a high pass filter connected between the input to the coil 64 and thedriving source. Therefore, as best shown in FIG. 6, the electric signal which is supplied to the time delay unit 50 from a suitable source 122, such as at the power amplifier of a sound amplifying system, is connected through an adjustable resistance 124 constituting a volume control and a series connected capacitor 126 which has a capacitance value suflicient to appreciably attenuate those frequencies in the sound waves which are less than 250 cycles per second. Since such low frequency sound waves need not be reverberated, it is preferablethat they be eliminated from the time delay system thereby to avoid the need for a suitable low-frequency woofer type loud-speaker. By eliminating such low frequencies, only a middle and high range 3,1ss,sse

7 speaker need be employed thereby appreciably reducing the cost of the system since woofer speakers and audio amplifiers having accurate frequency response in the low-frequency range of 250 cycles and less are extremely expensive.

The time delay unit 50 shown in FIGS. 3, 4 and 5 is adapted for use in a single channel system. However, a mechanical time delay device embodying the teachings of the present invention also finds application in multiple channel systems such as the dual channel stereo systems now in vogue. Referring to FIG. 7 there is shown, an electromechanical time delay device 130 which embodies the teachings of'the present invention and which is particularly adapted for use in a two-channel stereo system. In accordance with an important feature of the present invention the stereo time delay device 130 includes a pair of driving electromagnets 132 and 135 which are respectively coupled through a pair of coil springs 135 and 136 and associated resilient damping blocks 137 and 138 to a single microphone or transducer unit 141) which converts the mechanical vibrations supplied thereto by both springs 135 and 136 into an electric current appearing in a circuit comprising leads 14-2 and 143. The driver units 132 and 134 are each identical to the driver unit65' in the time delay device 50. Moreover, the springs 135 and 136 and associated dampers are also identical with the exception that the output ends thereof are cut at an angle so as to lie flush with the surface of the diaphragm 145 of the microphone unit 140. The springs 135 and 13s and associated damping units, as best shown in FIG. 8, are attached to separate diaphragms 145 and 147 in the microphone unit 140. Both of the diaphragms 145 and 147 partially cover both pole faces 149 and 150 of the U-shaped permanent magnet 151 of the microphone unit as best shown in FIG 8. Therefore, there is no mechanical loading or intercoupling between the springs 135 and 136 and simple addition of the two signals is effected in the magnetic circuit of the magnet 151 as the reluctance thereof is varied by the respective vibrations of the magnetic diaphragms 145 and 147. Intermodulation distortion is thus minimized in the device 130.

As shown in FIG. 9 it is preferable that the signals supplied to the unit 130 be coupled to the separate drivers 132 and. 134 through respective volume control rheostats 152 and 154 and high pass coupling capacitors 156 and 158, respectively, for the reasons set forth hereinabove in connection with FIG; 6.

Referring to FIG. 10, in order to connect the electromechanical time delay device 139 into a stereo system, signals are extracted from the A and B output channels of the two-channel audio amplifier 160 and supplied to the input of the unit 130, preferably through a volume control and high pass filter as illustratedin FIG 9. The separate A and B signals are, of course, also used to drive the separate A and B channel speaker systems 162 and 164 which are normally connected in the system and which are illustrated as constituting in each case a single loud-speaker. However, it will be understood that in most stereo applications high-fidelity is desired and, therefore, multiple speakers are used in order to provide a high-quality frequency response throughout the audio range for'each channel. This, however, is not necessary in the reverberant effect-producing system since the low frequency signals are filtered out. Accordingly, the tapped off A and B signals are separately delayed in the time delay device 131 and coupled to the microphone portion thereof where they are added together and supplied to a suitable audio amplifier 132. The composite time delayed sound wave is then used to drive a single, mid-high frequency range speaker 134 which is preferably positioned midway between the two speaker systems 162 and 164. The auxiliary speaker 134, when thus located, not only provides the necessary reverberation effects, but in addition it alleviates the so-called hole in the middle condition which sometimes occurs in stereo systems.

While the present invention has been described in controlled predetermined time interval, comprising a first electromagnetic device having a member movable along a linear path in accordance with the'waveform of an electric current supplied thereto, a helical coil spring secured at one end to said movable member, a second electromagnetic device for producing an electric current having a waveform corresponding to mechanical vibrations supplied thereto, means for securing the other end of said spring to said second electromechanical device to impart mechanical vibrations thereto, and a resilient damping member partially compressed within said spring, said damping member extending substantially throughout the length of said spring.

2. The apparatus set forth in claim 1 wherein said damping member engages said spring only at spaced intervals along said spring thereby to permit the intermediate portions of said spring to vibrate substantially independently of said damping member.

3. A time delay device for electric current signals having frequency components within the audio range, comprising a first electromagnetic device having a diaphragm portion movable along a substantially linearpath in response to an electric current signal supplied thereto, a helical coil spring bonded at one end to said diaphragm portion, a second electromagnetic device having a diaphragm portion movable along a substantially linear path to produce an electric current signal corresponding to the mechanical vibration of said diaphragm portion thereof, the other end of said coil spring being bonded to the diaphragm portion of said second electromagnetic device, an elongated resilient damping block mounted within said spring in partial transverse compression, said block engaging said spring only at spaced apart intervals along said spring, said intervals being less than one turn of said spring.

4. The combination of claim 3 wherein said damping block is bonded at one end thereof to said diaphragm portion of said second electromagnetic device.

5. For use in a system for synthesizing sound reverberation effects, the combination of a helical spring, means for impressing mechanical vibrations upon one end of said spring, means connected to the other end of said spring for converting mechanical vibrations thereof into an electric signal, resilient damping means connected to said spring substantially throughout the length thereof to retard the transmission of mechanical vibrations from one end of said spring to the other, said damping means comprising a unitary resilient member connected at spaced intervals to said spring, and said unitary member being a resilient bar compressed within said spring.

6. For use in a system for synthesizing sound reverberation effects, the combination of a helical spring, means for impressing mechanical vibrations upon one end of said spring, means connected to the other end of said spring for converting mechanical vibrations thereof into an electric signal, resilient damping means connected to said spring substantially throughout the length thereof to retard the transmission of mechanical vibrations from one end of said spring to the other, said damping means comprising a unitary resilient member connected at spaced intervals to said spring, said unitary member being a resilient bar compressed within said spring, and said bar being formed of a sponge-like elastomer.

1 to retard the transmission of mechanical vibrations from one end of said spring to the other, said damping means comprising a unitary resilient member connected at spaced intervals to said spring, said unitary member being a resilient bar compressed within said spring, said bar being formed of a sponge-like elastomer, and said bar being rectangular in cross-section, the unstressed diagonal dimension thereof exceeding the internal diameter of said coil and the side dimensions being less than the internal diameter of said coil whereby said bar engages said coil only along the corner edges of said bar.

8. For use in a system for synthesizing sound reverberation eifects, the combination of a helical spring, means for impressing mechanical vibrations upon one end of said spring, means connected to the other end of said spring for converting mechanical vibrations thereof into an electric signal, and resilient damping means connected to said spring substantially throughout the length thereof to retard the transmission of mechanical vibrations from one end of said spring to the other, said damping means comprising a unitary resilient member connected at spaced intervals to said spring, and a high pass filter means connected between said time delay means and said means for impressing mechanical vibrations upon one end of said spring.

9. Time delay apparatus for use in a multiple channel system, comprising a plurality of first electromagnetic devices each having a member movable in accordance with the waveform of an electric signal supplied thereto, means for supplying electric signals to said first electromagnetic devices, a plurality of helical coil springs respectively connected to said movable members, a second electromagnetic device for producing an electric current corresponding to the total of a plurality of mechanical vibrations supplied thereto, means connecting the other ends of said springs to said second electromagnetic device to impart mechanical vibrations thereto, and said second electromagnetic device comprising a single magnetic circuit and a plurality of diaphragm members arranged in parallel relationship in said circuit whereby the reluctance of said circuit is dependent upon the positions of said diaphragrns and said other ends of said springs are respectively connected to said 'diaphragrns.

10. Time delay apparatus for use in a multiple channel system, comprising a plurality of first electromagnetic devices each having a member movable in accordance with the waveform of an electric signal supplied thereto, means for supplying electric signals to said first electromagnetic devices, a plurality of helical coil springs respectively connected to said movable members, a second electromagnetic device for producing an electric current corresponding to the total of a plurality of mechanical vibrations supplied thereto, and means connecting the other ends of said springs to said second electromagnetic device to impart mechanical vibrations thereto, said second electromagnetic device comprising single magnetic circuit and a plurality of diaphragm members arranged in parallel relationship in said circuit whereby the reluctance of said circuit is dependent upon the positions of said diaphragms and said other ends of said springs are respectively connected to said diaphragms, and a plurality of resilient damping blocks respectively compressed Within said springs.

References Cited by the Examiner UNITED STATES PATENTS 1,947,621 2/34 Schreiber 179-1 2,230,836 2/41 Hammond "1,79-1 2,437,445 3/48 Stack 333-- 2,493,638 1/50 Olson 179-1 2,768,235 10/56 Knoblaugh 179--1 2,819,348 1/58 Bogert 179-100.1 2,852,604 9/58 MacCutcheon 179-1 2,978,543 4/61 Kennedy 179-1001 3,048,072 8/62 Hanert 841.24

ROBERT H. ROSE, Primary Examiner. WILLIAM C. COOPER, Examiner. 

1. APPARATUS FOR DELAYING AN ELECTRIC SIGNAL FOR A CONTROLLED PREDETERMINED TIME INTERVAL, COMPRISING A FIRST ELECTROMAGNETIC DEVICE HAVING A MEMBER MOVABLE ALONG A LINEAR PATH IN ACCORDANCE WITH THE WAVEFORM OF AN ELECTRIC CURRENT SUPPLIED THERETO, A HELICAL COIL SPRING SECURED AT ONE END TO SAID MOVABLE MEMBER, A SECOND ELECTROMAGNETIC DEVICE FOR PRODUCING AN ELECTRIC CURRENT HAVING A WAVEFORM CORRESPONDING TO MECHANICAL VIBRATIONS SUPPLIED THERETO, MEANS FOR SECURING THE OTHER END OF SAID SPRING TO SAID SECOND ELECTROMECHANICAL DEVICE TO IMPART MECHANICAL VIBRATIONS THERETO, AND A RESILIENT DAMPING MEMBER PARTIALLY COMPRESSED WITHIN SAID SPRING, SAID DAMPING MEMBER EXTENDING SUBSTANTIALLY THROUGHOUT THE LENGTH OF SAID SPRING. 